Stewart Marshall

Global carbon exchange and methane emissions from natural wetlands: Application of a process-based model

Wetlands are one of the most important sources of atmospheric methane (CH 4 ), but the strength of this source is still highly uncertain. To improve estimates of CH 4 emission at the regional and global scales and predict future variation requires a process-based model integrating the controls of climatic and edaphic factors and complex biological processes over CH 4 flux rates. This study used a methane emission model based on the hypothesis that plant primary production and soil organic matter decomposition act to control the supply of substrate needed by methanogens ; the rate of substrate supply and environmental factors, in turn, control the rate of CH 4 production, and the balance between CH 4 production and methanotrophic oxidation determines the rate of CH 4 emission into the atmosphere. Coupled to data sets for climate, vegetation, soil, and wetland distribution, the model was used to calculate spatial and seasonal distributions of CH 4 emissions at a resolution of 1° latitude x 1° longitude. The calculated net primary production (NPP) of wetlands ranged from 45 g C m -2 yr -1 for northern bogs to 820 g C m -2 yr -1 for tropical swamps. CH 4 emission rates from individual gridcells ranged from 0.0 to 661 mg CH 4 m -2 d -1 , with a mean of 40 mg CH 4 m -2 d -1 for northern wetland, 150 mg CH 4 m -2 d -1 for temperate wetland, and 199 mg CH 4 m -2 d -1 for tropical wetland. Total CH 4 emission was 92 Tg yr -1 . Sensitivity analysis showed that the response of CH 4 emission to climate change depends upon the combined effects of soil carbon storage, rate of decomposition, soil moisture and activity of methanogens.

Consumption of atmospheric methane by soils: A process‐based model

A process-based model for the consumption of atmospheric methane (CH4) by soils was developed to identify the most important factors affecting uptake rates and to determine whether the current uncertainties in the estimated size of the global soil sink might be reduced. Descriptions of diffusion and microbial oxidation processes, which together determine the CH4 flux, were included. The results suggest that the global sink strength lies within the range 20–51 Tg yr−1 CH4, with a preferred value of 38 Tg yr−1 CH4. Dry tropical ecosystems account for almost a third of this total. Here microbial activity rather than diffusion is limiting uptake. It is also in these areas that the impact of any intensification in agriculture will be the most pronounced, with a possible future reduction in uptake in excess of 3 Tg yr−1 CH4. This is in contrast to the overall impact of global warming, which is expected to leave the size of the global soil sink relatively unchanged.

Regional estimates of carbon sequestration potential: linking the Rothamsted carbon model to GIS databases

Abstract Soil organic matter (SOM) represents a major pool of carbon within the biosphere. It is estimated at about 1400 Pg globally, which is roughly twice that in atmospheric CO2. The soil can act as both a source and a sink for carbon and nutrients. Changes in agricultural land use and climate can lead to changes in the amount of carbon held in soils, thus, affecting the fluxes of CO2 to and from the atmosphere. Some agricultural management practices will lead to a net sequestration of carbon in the soil. Regional estimates of the carbon sequestration potential of these practices are crucial if policy makers are to plan future land uses to reduce national CO2 emissions. In Europe, carbon sequestration potential has previously been estimated using data from the Global Change and Terrestrial Ecosystems Soil Organic Matter Network (GCTE SOMNET). Linear relationships between management practices and yearly changes in soil organic carbon were developed and used to estimate changes in the total carbon stock of European soils. To refine these semi-quantitative estimates, the local soil type, meteorological conditions and land use must also be taken into account. To this end, we have modified the Rothamsted Carbon Model, so that it can be used in a predictive manner, with SOMNET data. The data is then adjusted for local conditions using Geographical Information Systems databases. In this paper, we describe how these developments can be used to estimate carbon sequestration at the regional level using a dynamic simulation model linked to spatially explicit data. Some calculations of the potential effects of afforestation on soil carbon stocks in Central Hungary provide a simple example of the system in use.

Resolution improvement of ERS scatterometer data over land by Wiener filtering

Abstract Multiplicative Wiener deconvolution has been applied to ERS scatterometer measurements obtained over land with the aim of improving their spatial resolution. The ERS scatterometer was launched to provide high-accuracy radar backscattering measurements over the sea surface for the purpose of monitoring marine wind velocity. However, ERS scatterometer data soon inspired an increasing interest for land and sea ice monitoring. The main shortcoming of these applications has been the coarse resolution of the device. This varies between 25 km2 and 46 km2 before ground processing, which results in normalization down to ∼48 km2 so that all the measurements can be used jointly in the wind vector retrieval. Nevertheless, for the case of perdurable sea ice and land scenes, measurements with 25-km resolution before ground processing can be selected to form images. As will be shown here, this finer resolution can be recovered for these images by using a linear Wiener filter. This restoration technique was tested on a large scene from Russia. The improvement can be observed in the definition of the line of the river Obs basin.